Colloidal Quantum Dots Research Articles

Rapid and large-scale synthesis of MoS2 via ultraviolet laser-assisted technology for photodetector applications

Two-dimensional transition metal dichalcogenide (TMDC) thin films have been extensively employed in microelectronics research. Molybdenum disulfide (MoS2), as one of prominent candidates of this class, has been applied in photodetectors, integrated electronic devices, gas sensing, and electrochemical catalysis, owing to its extraordinary optoelectronic, chemical, and mechanical properties. Synthesis of MoS2 crystal film is the key to its application. However, the reported technology revealed several drawbacks, containing limited surface area, prolonged high-temperature environment, and unsatisfying crystallinity. In order to enhance the convenience of MoS2 applications, there is a pressing need for optimized fabrication technology, which could be quicker, with a large area, with adequate crystallinity and heat-saving. In this work, we presented an ultraviolet laser-assisted synthesis technology, accomplishing rapid growth (with the growth rate of about 40 μm s−1) of centimeter-scale MoS2 films at room temperature. To achieve this, we self-assembled a displaceable reaction chamber system, coupled with krypton fluoride ultraviolet pulse laser. The laser motion speed and trajectory could be customized in the software, allowing the maskless patterning of crystal films. As application, we exhibited a photodetector with the integration of synthesized MoS2 and lead sulfide colloidal quantum dots (PbS CQDs), displaying broadband photodetection from ultraviolet, visible to near-infrared spectrum (365–1550 nm), with the detectivity of 109–1010 Jones, and the rising time of 0.2–0.3 s. This work not only demonstrated a high-process-efficiency synthesis of TMDC materials, but also has opened up new opportunities for ultraviolet laser used in optoelectronics.

Электрофизические и температурные характеристики тонких слоёв квантовых точек Ag2S

This paper presents a study of the electrical properties of colloidal silver sulfide quantum dots thin films (Ag2S/SiO2 QDs) and silver sulfide quantum dots decorated with Au plasmon nanoparticles (Ag2S/SiO2/Au QDs). A study of the conductivity temperature dependences was carried out in the temperature range from 300 to 360 K. The activation energy values were obtained from linear approximations of the current-voltage characteristics in Arrhenius coordinates. It has been shown that decorating Ag2S/SiO2 QDs with Au plasmon nanoparticles leads to an increase in the band gap from 0.29 to 0.89 eV. In this work, the ideality factor is calculated and the main conductivity mechanisms of the presented thin-film structures are determined. It has been shown that decorating Ag2S/SiO2 QDs with Au plasmon nanoparticles leads to a change in the conductivity type. According to the Mott-Gurney model, the charge carriers mobility is calculated.

Fluorescence Enhancement of CdS:Ag Quantum Dots Co-Assembled with Au Nanoparticles in a Hollow Nanosphere Form.

Colloidal quantum dots (QDs) have exceptional fluorescence properties. Overcoming aggregation-induced quenching and enhancing the fluorescence of colloidal QDs have remained a challenging issue in this field. In this study, composite hollow nanospheres composed of Au nanoparticles (NPs) and CdS:Ag-doped QDs were successfully constructed through controlled microemulsion-based cooperative assembly. This method harnessed the localized surface plasmon resonance (LSPR) effect of Au NPs nearby doped QDs, resulting in enhanced doped QD fluorescence and the observation of the Purcell effect. The composite hollow nanospheres show a fluorescence enhancement compared to that of the pure CdS:Ag QDs. The enhanced fluorescence was demonstrated to come from the synergetic enhancement of the absorption and emission transition of the doped QDs. This approach provides a feasible technological pathway to address the challenge of improving the fluorescence performance of the doped QDs.

Optimizing Thin Films and Device Structures for the Design of PbS Colloidal Quantum Dots Near-Infrared Photodetectors

Optimizing Thin Films and Device Structures for the Design of PbS Colloidal Quantum Dots Near-Infrared Photodetectors

Narrowing the photoluminescence bandwidth of InP‐based colloidal quantum dots through photon‐triggered isolation

AbstractThe optimization of photoluminescence (PL) spectral bandwidths in InP‐based colloidal quantum dots (QDs) faces limitations with traditional synthetic methods. This study introduces a novel approach utilizing light‐induced thiolate ligand detachment to selectively precipitate QDs within an ensemble, triggered by photons whose energy matches the red tail of the band‐edge absorption peak. We demonstrate that incorporating benzoquinone as an electron acceptor under inert conditions crucially enhances the efficiency of photoexcited hole‐induced ligand detachment. Through careful optimization of laser exposure conditions, we successfully narrowed the PL bandwidth of InP/ZnSe/ZnS QDs from 39 to 35 nm. Our findings offer significant insights into the development of high‐performance QD‐based displays, promising advancements in color purity.

Synergistic selenium doping and colloidal quantum dots decoration over ZnIn2S4 enabling high-efficiency photoelectrochemical hydrogen peroxide production

Photoelectrochemical (PEC) water splitting to value-added hydrogen peroxide (H2O2) production is more promising than the traditional O2 evolution. However, enabling efficient PEC H2O2 generation is still challenging due to competitive two-/four-electron water oxidation pathways. In this work, ZnIn2S4 (ZIS) photoanodes were engineered by Se doping and colloidal quantum dots (QDs) modification to boost the PEC H2O2 evolution efficiency. Morphology and elemental studies testify the successful Se doping in ZIS and the anchoring of QDs on ZIS-Se photoelectrodes. Photoinduced carrier kinetics investigation verifies the optimized band bending, suppressed charge recombination, and promoted charge transfer in as-prepared ZIS-Se and ZIS-Se/QDs photoanodes, exhibiting inhibited four-electron O2 evolution and facilitated two-electron H2O2 production during PEC water oxidation, as evidenced by the density functional theory (DFT) calculations. Accordingly, the Se-doped and QDs-decorated ZIS photoelectrodes demonstrate a gradually less upward band bending and improved photo-excited hole transfer to the surface, delivering a maximum H2O2 production rate of 1.32 μmol min−1 cm−2 with a Faraday efficiency of 86 % at 1.23 V versus reversible hydrogen electrode (RHE) under one sun illumination.

Perovskite Colloidal Quantum Dots with Tailored Properties: Synthesis Strategies and Photovoltaic Applications

Perovskite Colloidal Quantum Dots with Tailored Properties: Synthesis Strategies and Photovoltaic Applications

Coupling of Infrared Active Colloidal Quantum Dots and Amorphous Selenium for Fast and Sensitive Photodetection

AbstractColloidal quantum dot (CQD) based infrared (IR) photodetectors offer facile wavelength tunability in the IR and low‐cost fabrication. However, owing to their large surface areas, CQDs intrinsically have significant surface traps critically affecting the speed of CQD photodetectors, typically mediated through tedious surface passivation efforts. In this report, an alternative strategy involving coupling of near‐IR photoactive lead sulfide CQDs with a thermally evaporated amorphous selenium (a‐Se) hole transport layer is proposed. By separating the detector into a photon absorbing CQD region and a charge transport a‐Se region, the study takes advantage of the extremely low noise, predominantly hole‐only transport process in a‐Se. A high 3 dB bandwidth of 2.5 MHz and a competitive specific detectivity of 2.5 × 1011 Jones at room temperature are demonstrated at 980 nm. This report serves as a first demonstration of strong coupling between an IR active CQD absorber and a‐Se, which paves the path to obtain fast and highly photoresponsive IR photodetection in the future.

Heterointerface Effects on Carrier Dynamics in Colloidal Quantum Dots and Their Application to Light-Emitting Diodes.

Colloidal quantum dots (QDs) are promising candidates for next-generation display technology because of their unique optical properties and have already appeared in the market as a high-end product. On the basis of their extraordinary properties, QD emissions with a given chemical composition can be tailored in a wide spectral window due to quantum size effects, which constitutes a key advantage of QDs in the display field. Specifically, investigations of structure-dependent and composition-dependent characterizations outside the quantum confinement effect have become an important part of practical applications. Therefore, from the perspective of designing nanostructures with well-defined heterointerfaces, strong quantum confinement effects with effective carrier confinement are desirable. Our results show that the photoluminescence (PL) intensity of CdSe/CdZnS core-shell QDs was enhanced 5.7 times compared with that of the CdSe core QDs. Supplementary analytical techniques involving transmission electron microscopy revealed the heterointerface configuration and composition distribution of the core and shell materials. The effects of the heterointerface on carrier dynamics in core-shell QDs were revealed by monitoring wavelength-dependent time-resolved PL. To further develop the QD light-emitting diodes (QD-LEDs), we produced an all-solution processed inverted QD-LEDs using CdSe/CdZnS core-shell QDs as the emitter. The electroluminescence spectrum of deep-red emissive QD-LEDs with CIE chromaticity coordinates of (0.68, 0.32) exhibited a peak at 638 nm.

Short-Wave Infrared Colloidal QD Photodetector with Nanosecond Response Times Enabled by Ultrathin Absorber Layers.

Ultrafast short-wavelength infrared (SWIR) photodetection is of great interest for emerging automated vision and spatial mapping technologies. Colloidal quantum dots (QDs) stand out for SWIR photodetection compared to epitaxial (In,Ga)As or (Hg,Cd)Te semiconductors by their combining a size-tunable bandgap and a suitability for cost-effective, solution-based processing. However, achieving ultrafast, nanosecond-level response time has remained an outstanding challenge for QD-based SWIR photodiodes (QDPDs). Here, record 4ns response time in PbS-based QDPDs that operate at SWIR wavelengths is reported, a result reaching the requirement of SWIR light detection and ranging based on colloidal QDs. These ultrafast QDPDs combine a thin active layer to reduce the carrier transport time and a small area to inhibit slow capacitive discharging. By implementing a concentration gradient ligand exchange method, high-quality p-n junctions are fabricated in these ultrathin QDPDs. Moreover, these ultrathin QDPDs attain an external quantum efficiency of 42% at 1330nm, due to a 2.5-fold enhanced light absorption through the formation of a Fabry-Perot cavity within the QDPD and the highly efficient extraction (98%) of photogenerated charge carriers. Based on these results, it is estimated that a further increase of the charge-carrier mobility can lead to PbS QDPDs with sub-nanosecond response time.

High Volumetric Energy Density Supercapacitor of Additive-Free Quantum Dot Hierarchical Nanopore Structure.

The high surface-area-to-volume ratio of colloidal quantum dots (QDs) positions them as promising materials for high-performance supercapacitor electrodes. However, the challenge lies in achieving a highly accessible surface area, while maintaining good electrical conductivity. An efficient supercapacitor demands a dense yet highly porous structure that facilitates efficient ion-surface interactions and supports fast charge mobility. Here we demonstrate the successful development of additive-free ultrahigh energy density electric double-layer capacitors based on quantum dot hierarchical nanopore (QDHN) structures. Lead sulfide QDs are assembled into QDHN structures that strike a balance between electrical conductivity and efficient ion diffusion by employing meticulous control over inter-QD distances without any additives. Using ionic liquid as the electrolyte, the high-voltage ultrathin-film microsupercapacitors achieve a remarkable combination of volumetric energy density (95.6 mWh cm-3) and power density (13.5 W cm-3). This achievement is attributed to the intrinsic capability of QDHN structures to accumulate charge carriers efficiently. These findings introduce innovative concepts for leveraging colloidal nanomaterials in the advancement of high-performance energy storage devices.

Highly Wavelength-Selective Self-Powered Solar-Blind Ultraviolet Photodetector Based on Colloidal Aluminum Nitride Quantum Dots.

Colloidal quantum dots are semiconductor nanocrystals endowed with unique optoelectronic properties. A major challenge to the field is the lack of methods for synthesizing quantum dots exhibit strong photo-response in the deep-ultraviolet (DUV) band. Here, a facile solution-processed method is presented for synthesizing ultrawide bandgap aluminium nitride quantum dots (AlN QDs) showing distinguished UV-B photoluminescence. Combined with the strong optical response in solar blind band, a solution-processed, self-powered AlN-QDs/β-Ga2O3 solar-blind photodetector is demonstrated. The photodetector is characterized with a high responsivity of 1.6mAW-1 under 0V bias and specific detectivity 7.60 × 10-11 Jones under 5V bias voltage with good solar blind selectivity. Given the solution-processed capability of the devices and extraordinary properties of AlN QDs, this study anticipates the utilization of AlN QDs will open up unique opportunities for cost-effective industrial production of high-performance DUV optoelectronics for large-scale applications.

Interfacial Heterojunction Enables High Efficient PbS Quantum Dot Solar Cells.

Colloidal quantum dots (CQDs) are promising optoelectronic materials for solution-processed thin film optoelectronic devices. However, the large surface area with abundant surface defects of CQDs and trap-assisted non-radiative recombination losses at the interface between CQDs and charge-transport layer limit their optoelectronic performance. To address this issue, an interface heterojunction strategy is proposed to protect the CQDs interface by incorporating a thin layer of polyethyleneimine (PEIE) to suppress trap-assisted non-radiative recombination losses. This thin layer not only acts as a protective barrier but also modulates carrier recombination and extraction dynamics by forming heterojunctions at the buried interface between CQDs and charge-transport layer, thereby enhancing the interface charge extraction efficiency. This enhancement is demonstrated by the shortened lifetime of carrier extraction from 0.72 to 0.46ps. As a result, the resultant PbS CQD solar cells achieve a power-conversion-efficiency (PCE) of 13.4% compared to 12.2% without the heterojunction.

The influence of solvent refractive index on the photoluminescence decay of thick-shell gradient-alloyed colloidal quantum dots investigated in a wide range of delay times.

Colloidal semiconductor quantum dots have many potential optical applications, including quantum dot light-emitting diodes, single-photon sources, or biological luminescent markers. The optical properties of colloidal quantum dots can be affected by their dielectric environment. This study investigated the photoluminescence (PL) decay of thick-shell gradient-alloyed colloidal semiconductor quantum dots as a function of solvent refractive index. These measurements were conducted in a wide range of delay times to account for both the initial spontaneous decay of excitons and the delayed emission of excitons that has the form of a power law. It is shown that whereas the initial spontaneous PL decay is very sensitive to the refractive index of the solvent, the power-law delayed emission of excitons is not. Our results seem to exclude the possibility of carrier self-trapping in the considered solvents and suggest the existence of trap states inside the quantum dots. Finally, our data show that the average exciton lifetime significantly decreases as a function of the solvent refractive index. The change in exciton lifetime is qualitatively modeled and discussed.

Effective Charge Collection of Electron Transport Layers for High-Performance Quantum Dot Infrared Solar Cells.

Infrared (IR) solar cells, capable of converting low-energy IR photons to electron-hole pairs, are promising optoelectronic devices by broadening the utilization range of the solar spectrum to the short-wavelength IR region. The emerging PbS colloidal quantum dot (QD) IR solar cells attract much attention due to their tunable band gaps in the IR region, potential multiple exciton generation, and facile solution processing. In PbS QD solar cells, ZnO is commonly utilized as an electron transport layer (ETL) to establish a depleted heterostructure with a QD photoactive layer. However, band gap shrinkage of large PbS QDs makes it necessary to tailor the behaviors of the ZnO ETL for efficient carrier extraction in the devices. Herein, the characteristics of ZnO ETL are efficiently and flexibly tailored to match the QD layer by handily adjusting the postannealing process of ZnO ETL. With a suitable temperature, the well-matched energy level alignment and suppressed trap states are simultaneously achieved in the ZnO ETL, effectively reducing the nonradiative recombination and accelerating the electron injection from the QD layer to ETL. As a consequence, a high-performance PbS QD photovoltaic device with power conversion efficiencies (PCEs) of 10.09% and 1.37% is obtained under AM 1.5 and 1100 nm filtered solar illumination, demonstrating a simple and effective approach for achieving high-performance IR photoelectric devices.

The Impact of Colloidal QD Science and Technology on the Display Industry

AbstractCongratulations to Moungi G. Bawendi, Louis E. Brus, and Aleksey Yekimov for winning the 2023 Nobel Prize in Chemistry “for the discovery and synthesis of quantum dots.” This is an outstanding achievement for them and for all of us who currently work or have worked on developing and commercializing colloidal quantum‐dot (QD) technology.

Recent Developments in Quantum Dot Patterning Technology for Quantum Dot Display

Colloidal quantum dot (QDs) have emerged as a crucial building block for LEDs due to their size-tunable emission wavelength, narrow spectral line width, and high quantum efficiency. Tremendous efforts have been dedicated to improving the performance of quantum dot light-emitting diodes (QLEDs) in the past decade, primarily focusing on optimization of device architectures and synthetic procedures for high quality QDs. However, despite these efforts, the commercialization of QLEDs has yet to be realized due to the absence of suitable large-scale patterning technologies for high-resolution devices., This review will focus on the development trends associated with transfer printing, photolithography, and inkjet printing, and aims to provide a brief overview of the fabricated QLED devices. The advancement of various quantum dot patterning methods will lead to the development of not only QLED devices but also solar cells, quantum communication, and quantum computers.

In-Synthesis Se-Stabilization Enables Defect and Doping Engineering of HgTe Colloidal Quantum Dots.

Colloidal Quantum Dots (CQDs) of mercury telluride (HgTe) hold particular appeal for infrared photodetection due to their widely tunable infrared absorption and good compatibility with silicon electronics. While advances in surface chemistry have led to improved CQD solids, the chemical stability of HgTe material is not fully emphasized. In this study, it is aimed to address this issue and identifies a Se-stabilization strategy based on the surface coating of Se on HgTe CQDs via engineering in the precursor reactivity. The presence of Se-coating enables HgTe CQDs with improved colloidal stability, passivation, and enhanced degree of freedom in doping tuning. This enables the construction of optimized p-i-n HgTe CQD infrared photodetectors with an ultra-low dark current 3.26 × 10-6 Acm⁻2 at -0.4V and room-temperature specific detectivity of 5.17 × 1011 Jones at wavelength ≈2 um, approximately one order of magnitude improvement compared to that of the control device. The stabilizing effect of Se is well preserved in the thin film state, contributing to much improved device stability. The in-synthesis Se-stabilization strategy highlights the importance of the chemical stability of materials for the construction of semiconductor-grade CQD solids and may have important implications for other high-performance CQD optoelectronic devices.

Synergetic Exterior and Interfacial Approaches by Colloidal Carbon Quantum Dots for More Stable Perovskite Solar Cells Against UV.

The achievement of both efficiency and stability in perovskite solar cells (PSCs) remains a challenging and actively researched topic. In particular, among different environmental factors, ultraviolet (UV) photons play a pivotal role in contributing to device degradation. In this work, by harvesting simultaneously both the optical and the structural properties of bottom-up-synthesized colloidal carbon quantum dots (CQDs), a cost-effective means is provided to circumvent the UV-induced degradation in PSCs without scarification on their power conversion efficiencies (PCEs). By exploring and optimizing the number of CQDs and the different locations/interfaces of the solar cells where CQDs are applied, a synergetic configuration is achieved where the photovoltaic performance drop due to optical loss is completely compensated by the increased perovskite crystallinity due to interfacial modification. As a result, on the optimized configurations where CQDs are applied both on the exterior front side as an optical layer and at the interface between the electron transport layer and the perovskite absorber, unencapsulated PSCs with PCEs >20% are fabricated which can maintain up to ≈94% of their initial PCE after 100h of degradation in ambient air under continuous UV illumination (5mWcm-2).

High-Performance Visible to Mid-Infrared Photodetectors Based on HgTe Colloidal Quantum Dots under Room Temperature.

HgTe colloidal quantum dots (CQDs) are one of few materials that can realize near-to-midwave infrared photodetection. And the quality of HgTe CQD directly affects the performance of photodetection. In this work, we optimize the method of synthesizing HgTe CQDs to reduce the defect concentration, therefore improving the photoelectric properties. The photodetector based on HeTe CQD can respond to the light from the visible to mid-infrared band. Notably, a photoresponse to 4000 nm light at room temperature is realized. The responsivity and detectivity are 90.6 mA W-1 and 6.9 × 107 Jones under 1550 nm light illumination, which are better than these of most reported HgTe CQD photodetectors. The response speed reaches a magnitude of microseconds with a rising time of τr = 1.9 μs and a falling time of τf = 1.5 μs at 10 kHz under 1550 nm light illumination.